1. Field of the Invention
The invention relates to a method and apparatus for measuring group delay of a device under test, more particularly to a method and apparatus for measuring group delay of a device under test that utilize a single-tone analog input signal.
2. Description of the Related Art
Group delay of most electronic devices will result in non-negligible influences. For example, in a data storage system, if group delay of an internal electronic device of the data storage system cannot not be managed, correct timing sequence during data reproduction cannot be ensured, which can result in incorrect decoding of data. Furthermore, for digital communication systems, if group delay cannot be properly processed, non-linear distortion of transmission signals cannot be avoided. As such, measurement of group delay of an electronic device is very important.
In a conventional method of measuring group delay (Tgd) of a device under test having a high cut-off frequency band, a multi-tone signal, which is a high frequency signal, is provided to the device under test. As shown in FIG. 1, the multi-tone signal, which is provided from a multi-tone input source, includes two high frequency components 11, 12. There exists a frequency difference (Δf) between the high frequency components 11, 12. For example, the high frequency components 12, 11 may be 40 MHz and 40.05 MHz, respectively. A phase difference (ΔP) between the high frequency components 11, 12 can be calculated by discrete Fourier transform using relevant analysis instruments after passing the device under test (DUT). As such, the group delay (Tgd) equal to −ΔP/Δf may be obtained accordingly.
However, in order to obtain a precise measurement, the analysis instruments used in the aforesaid method must include a high-speed digitizer for high-speed digitizing of the high frequency components 11, 12, and a high-resolution measuring device for calculating the phase difference (ΔP). Unfortunately, the high-speed digitizer and the high-resolution measuring device are very expensive and use of the same results in high costs.